It's the superstar of the coral world. Australia's Great
Barrier Reef—the largest system of its kind on Earth—is
everything a reef should be: a fantasia of hard and soft
coral teeming with sea turtles, giant clams, sea anemones,
spiny lobsters, shrimp, squid, and fish that look as if
they've rolled across a Peter Max palette.

Australian Environment Minister Robert Hill recently reported
that the reef generally is in good shape—protected in part
by its sheer gargantuan size. But conservationists on the
island continent and elsewhere are sounding alarms over
the future of this 1,250-mile (2,000-km) underwater wonderland.

Ominous developments over recent years include damage by
overzealous fishermen, repeated invasions of coral-eating
starfish, and that deadly affliction of reefs around the
globe: coral bleaching. All of this—including the starfish
plague—is more or less directly related to human activities
in the opinion of some leading experts.

The executive director of the Australian Conservation Foundation,
Don Henry, has labeled the various threats to the reef,
a United Nations-designated World Heritage Area , as "extremely
serious," and cautioned that it is at risk of being put
on the UN's endangered list.

Last year, four respected scientists warned the UN World
Heritage Bureau that the reef will "steadily degrade" if
the current management regime continues. They said the corals
face "slow death" from "a thousand cuts," and called for
an independent assessment of the threats.

An even direr warning came last October from the Geneva-based
World Wildlife Fund for Nature, which predicted that rising
sea temperatures attributed to global warming could destroy
the reef entirely by 2010.

UNDERWATER OLYMPIC FLAME

Along with the famed landmark Uluru (previously called Ayers
Rock), the Great Barrier Reef is the pride of Australia.

In June, the Olympic flame made a short lap through its
sapphire blue waters on its way to Sydney for the 2000 Olympic
Games. The swim was an historic first for the Olympic flame,
which was carried by a scuba diver in a specially designed
torch.

Protected as a marine park since 1975, the reef encompasses
about 135,000 square miles (351,000 sq km)—an area larger
than Great Britain. It's so large that it can be seen from
satellites.

The largest system of coral and associated plants and animals
in the world, the reef actually is a formation of 2,900
separate reefs off of Australia's northeast coast. Its waters
are home to 1,500 species of fish, 400 kinds of corals,
and 4,000 species of mollusks.

Some of these waters off the state of Queensland have become
increasingly murky during the past decade or so. One study
found that runoff from cattle grazing lands and sugar-cane
fields flowing into Queensland's rivers washes 16.5 million
tons of sediment into the Coral Sea each year. The silt
smothers the polyps—the tiny animals that build the coral—on
the inner reefs. The runoff in this study also contained
nearly 85,000 tons of nitrogen and 11,000 tons of phosphorous,
much of it from fertilizers used on farms.

Under certain wind and tidal conditions, this mud soup can
carry harmful chemicals 125 miles (201 kilometers) offshore,
where nitrogen and phosphorous enhance the growth of phytoplankton,
a type of algae. The green goo blocks sunlight needed to
nurture coral and other reef creatures, and damages the
polyps' hard exterior skeleton—making it weaker and more
prone to damage from storms.

CORAL-EATING STARFISH

The issue of agricultural runoff is contentious, especially
in the farming areas. A long-term reef monitoring project
begun in 1992 by the Australian Institute of Marine Science
(AIMS) thus far has not established a statistical correlation
between human activities and the nutrient content of sediments.
However, the institute noted that most nutrients probably
don't wind up in the layers of silt.

Increased nutrients in the water, along with higher salinity
and warmer temperatures, are suspects in the most recent
invasion of crown-of-thorn starfish, which feed on polyps.
The latest incursion is the third in recent decades, prompting
a debate as to whether their arrivals are entirely natural,
or are at least partly brought on by human activities. The
nutrient-rich runoff that stimulates algae growth also contains
microscopic diatoms and dinoflagellates that provide nourishment
for the starfish.

Conservationists argue that overfishing on the reefs is
upsetting the natural balance. Anchors and chains dropped
by commercial trawlers and weekend sailors take a further
toll—as do the coral chunks that are inevitably broken off
or otherwise damaged by the more careless sight-seeing snorklers
and scuba divers.

Perhaps most ominous—and possibly the least controllable
of the threats—is coral bleaching. Recent episodes, including
a massive 1998 outbreak, are thought by some to have been
brought on by global warming.

The corals' rich colors are provided by tiny algae called
zooxanthellae, which live in symbiotic relationships with
coral polyps. When the polyps come under various kinds of
stress, including rising sea temperatures, they expel their
neighbors and turn white—the rough equivalent of running
a fever. Bleaching isn't necessarily fatal unless the stress
continues, in which case the polyps may starve to death.
An especially severe episode of bleaching in 1983 killed
95 percent of the corals off in another part of the world:
the Galapagos Island.

GREAT BARRIER LAWN?

AIMS believes that another major bleaching episode may have
been prevented last year by a lucky event in the region:
a heavy summer downpour that lowered the sea temperature
and provided two other bleaching preventatives at just the
right time: cloud cover and strong winds. Up until then,
according to Great Barrier Reef Marine Park Authority scientist
Ray Berkelmans, the summer weather had been "a perfect recipe
for a bleaching disturbance."

Last year, AIMS long-term monitoring project leader Hugh
Sweatman reported that despite the 1998 bleaching episode
and the abundance of starfish in certain locales, reefs
in other areas have shown net increases in hard coral over
the past two years. But he said the future is uncertain.

In one nightmare scenario, naturally occurring coral enemies
such as cyclones and flood plumes, along with human interference
such as overfishing and higher nutrient concentrations,
could kill off vast areas of corals—opening those areas
up to invasions of seaweed. In sufficient quantities, fish,
shrimp, and urchins that normally feed on these hardy plants
could be overwhelmed.

In case of a massive coral die-off, "All going well, corals
can become dominant again over about a decade," said Terry
Done, project leader of AIMS' Sustaining Coral Reefs project.
"However, we are concerned that the balance can be tilted
in favor of the seaweeds long-term."

The Great Barrier Reef could become the Great Barrier Lawn.

Eye in the Sky is a weekly series that brings you the story behind the headlines using satellite imagery, remote sensing, aerial photography, and maps. This feature is developed by National Geographic News with the sponsorship of the National Imagery and Mapping Agency (NIMA) and Earth-Info. Check out maps and imagery at http://www.earth-info.org.

 Found mostly in shallow temperate or tropical ocean waters, coral reefs are the largest formations made on Earth by living organisms.
 Coral Reefs are the handiwork of small marine animals called polyps, which manufacture limestone cups to protect their soft bodies.
 When living bits of coral die, their calcified remains bond together. Over hundreds and thousands of years they form massive reefs.
 Some experts estimate that 10 percent of the Earth's 400,000 square miles (1 million sq km) of coral reefs have been seriously damaged. Thirty percent may die within the next two decades, and by the year 2050, another 30 percent may perish.

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CORAL SUNSCREEN?

Coral is not only beautiful to behold. Its utility in several products, including sunscreen, cosmetics, and a substitute for human bone, is still being fully appreciated.

Living coral oozes a clear mucus substance that helps protect the animal against the sun's ultraviolet rays. Several years ago two coral experts at the Australian Institute of Marine Science (AIMS) in Townsville synthesized and patented the protective chemicals. Now the institute has partnered with an Australian company, Sunscreen Technologies, to develop a commercial product that they believe will become available on the world market within five years.

"We believe that within a very few years the coral sunscreen could displace the range of UV-B blockers now in use," said AIMS executive Peter Isdale. "The future market in global terms for the new compound and its formulations is estimated at several hundred million dollars each year."

Since the key ingredients can be synthesized, actual coral won't have to be sacrificed to prevent human sunburning; and the profits would be shared with the Institute to further Australian marine research.

Slightly more problematical from a coral's point of view is its use as bone substitute in reconstructive surgery. The interconnected pores of specially treated warm-water corals allow adjacent living bone to send new blood vessels and bone tissue into the coral maze, creating a strong bond of new bone. This saves having to harvest bone grafts form the patients themselves.

However, the small amounts of coral needed for such use pose little threat to the survival of the world's coral reefs, since one coral head weighing 150 to 200 pounds provides enough material for hundreds of bone grafts.